Heavy-contour 18" barrel is machined from high-grade stainless steel alloy, with a non-reflective matte black Teflon exterior finish. Chambered for 5.56mm NATO ammunition, 6-groove button rifled with a 1-8" twist. Extra length gives additional velocity for better potential long-range accuracy, with M4 feed ramps in the barrel extension and a rifle-length gas system for an extra measure of reliability. Compatible with any standard AR-15 upper.